The long term objective of this project is to understand at the cellular level the effect of mechanical and electrical stimuli on bone growth and remodeling. The short term goals are (1) to examine the effects of mechanical and electrical stimuli on cell proliferation and collagen synthesis and (2) to test the hypothesis that these effects are mediated by perturbations of the cell membrane. The cellular models used are: chick epiphyseal chondrocytes, rat calvaria cells, and clonal cell lines from rat osteosarcoma recently established in our laboratory. Some of these lines possess pronounced osteoblastic characteristics. Mechanical stimuli of about 100 mm Hg are applied by increasing intermittently the hydrostatic pressure above the cells in culture. Electrical perturbations, producing micro A currents in the culture media, are applied via electromagnetic fields. The cell proliferation parameters measured are: induction of ornithine decarboxylase, DNA synthesis (using 3H-thymidine incorporation), labelled mitotic figures or mitotic index. Collagen synthesis is measured as total hydroxyproline in cell and media hydrolysates or collagenase digestible radioactivity following exposure of cultures to 3H-proline. Collagen types are assessed by acrylamide gel electrophoresis and CM cellulose chromatography of CNBr fragments. Membrane perturbation related parameters to be measured are: 3',5' cyclic AMP accumulation, Na ion permeability, assessed by 86Rb ion uptake, and the effect of Na ion, K ion and Ca2 ion ionophores and flux inhibitors on the mechanical/electrical effects. The findings accumulated so far show cell cycle-dependent effects of mechanical and electrical perturbations on cell proliferation and point to increased Na ion permeability as the potential mechanism for signal transduction.